Assessment of Endothelial Glycocalyx Dysfunction and Impaired Microcirculatory Perfusion During Cardiac Surgery to Improve Prediction of Post-operative Acute Kidney

Study design: Prospective cohort study.

The investigators will recruit 70 elective patients undergoing CABG surgery with and without cardiopulmonary bypass (CPB), with blood and urine sampling and assessment of microcirculatory perfusion by IDF in pre- peri- and post-operative periods, with informed written consent. The investigators have completed a feasibility study with successful recruitment and data collection at all time points and the current protocol and patient material have been reviewed by a patient representative.

Blood and urine samples will be analysed to consider markers of endothelial glycocalyx degradation (including syndecan-1 (SDC1)), endothelial activation (including thrombomodulin (TM)), and markers of renal tubular stress (NephroCheck).

Sublingual microcirculatory perfusion assessed by IDF imaging is painless and low risk and participant acceptability has been confirmed during the feasibility study. The process involves using a small handheld probe to gently press on the underside of the tongue and takes 3-10 minutes. Four video clips of 10s will be taken from each participant from different sites within the sublingual area. Videos will be exported as pseudonymised files for analysis. Image collection and analysis will be performed in accordance with international consensus recommendations, using a CytoCam video-microscope (Braedius Medical B.V., Huizen, The Netherlands). Images will be analysed using a dedicated software tool (Automated Vascular Analysis V.3.02, Microvision Medical, The Netherlands). Data generated will include flow and density-based measures of the microcirculation, including Perfused Vessel Density (PVD) and Microcirculatory Flow Index (MFI).

Peri-operative sampling and imaging will occur at predefined surgical time-points, in keeping with previous studies and informed by the feasibility study. Time-points were selected in anticipation of the most informative results, including point of peak "reperfusion" after final surgical anastomosis, and to minimise participant inconvenience (existing arterial line and urinary catheter tubing will be used) and to avoid surgical disruption and delays (IDF is quicker during anaesthesia and previous studies have shown negligible change between baseline and assessment immediately after anaesthesia prior to surgery).